Scale of local magnitudes ML for earthquakes in the Terek-Caspian trough

Abstract

A scale (calibration function) to determine the local magnitude ML of earthquakes with epicenters in the central part of the Terek-Caspian trough has been developed. The scale is based on a formula that takes into account attenuation and geometric divergence with distance for the maximum amplitudes of the simulated recordings of the short-period Wood-Anderson instrument. To calculate it, a sample of 64 earthquakes that occurred in 2020–2022, during the period of activation in the Black Mountains in the Chechen Republic, was compiled. Earthquakes were recorded by 58 stations in the distance range of 25–526 km, located around the epicenters in various geological and tectonic area. The Magscale program developed at the GS RAS based on methodological recommendations set out in the New Manual for Observatory Practice (NMSOP) was used for the calculation. The values of the coefficients of the equation, which characterize the attenuation in the crust and upper mantle, are obtained. The station corrections are calculated. Their use made it possible to reduce the scale deviations from ±0.26 to ±0.15. The areal distribution of residuals probably reflects the geological features of the area.